Mcm5 Represses Endodermal Migration through Cxcr4a-itgb1b Cascade Instead of Cell Cycle Control.

Yu Zhang,Xindong Liu,Min Liu,Shurong Li,Min Yang,Jiamin Xia,Bingyu Chen,Yu Ou,Xiaoping Yu,Yi Feng,Bingyin Su,Sizhou Huang

doi:10.3390/biom12020286

Abstract

Minichromosome maintenance protein 5 (MCM5) is a critical cell cycle regulator; its role in DNA replication is well known, but whether it is involved in the regulation of organogenesis in a cell cycle-independent way, is far from clear. In this study, we found that a loss of mcm5 function resulted in a mildly smaller liver, but that mcm5 overexpression led to liver bifida. Further, the data showed that mcm5 overexpression delayed endodermal migration in the ventral–dorsal axis and induced the liver bifida. Cell cycle analysis showed that a loss of mcm5 function, but not overexpression, resulted in cell cycle delay and increased cell apoptosis during gastrulation, implying that liver bifida was not the result of a cell cycle defect. In terms of its mechanism, our data proves that mcm5 represses the expression of cxcr4a, which sequentially causes a decrease in the expression of itgb1b during gastrulation. The downregulation of the cxcr4a-itgb1b cascade leads to an endodermal migration delay during gastrulation, as well as to the subsequent liver bifida during liver morphogenesis. In conclusion, our results suggest that in a cell cycle-independent way, mcm5 works as a gene expression regulator, either partially and directly, or indirectly repressing the expression of cxcr4a and the downstream gene itgb1b, to coordinate endodermal migration during gastrulation and liver location during liver organogenesis.

Highlights

The minichromosome maintenance (MCM) 2–7 complex, the crucial component of the DNA replication licensing system [1], acts as the eukaryotic DNA replicative helicase during the cell cycle, in normal development and tumorigenesis [2,3]
Since the quantity of Minichromosome maintenance protein 5 (MCM5) is largely more than that required for DNA replication [1], and mcm5 is expressed ubiquitously in proliferating cells, including in the liver of zebrafish [9] (Figure S1), we propose that MCM5 plays an extra role beside DNA duplication regulation during liver development
The data showed that embryos injected with mcm5 mRNA displayed liver bifida and liver reversal (Figure 1K–N), but no liver localization defects were observed in the mcm5−/− embryos or in the controls (Figure 1 J,N)

Summary

Introduction

The minichromosome maintenance (MCM) 2–7 complex, the crucial component of the DNA replication licensing system [1], acts as the eukaryotic DNA replicative helicase during the cell cycle, in normal development and tumorigenesis [2,3]. Previous studies demonstrated that Mcm proteins are loaded onto DNA in 20-fold excess over the number of replication origins [4], but that normal replication is still maintained when. Mcm proteins are decreased [5] This raises the possibility that an additional role of MCM family members exists besides their role in normal DNA replication regulation. Early research has demonstrated that the excess of MCM complex, allows dormant origins of DNA replication when the cell is under replication stress [6]. A detailed analysis showed that most dormant DNA replication origins are within highly transcribed genes [7], implying that most of the components of ORC, including the members of the 4.0/).

Methods

Results

Conclusion